Self-aligned silicide (salicide) technology is required in modern integrated circuit and semiconductor device fabrication to lower the resistance of polysilicon gates, sources and drains to reduce RC delay, i.e., the gate speed performance index wherein less delay produces increased gate speed performance. An example of a well known silicide technology is cobalt silicide (CoSi2). CoSi2 technology is commonly used for sub quarter micron and beyond technology. However, the agglomeration effect of CoSi2 on very narrow line polysilicon gates that are less than ˜42 nanometers, often limits its extendibility to the fabrication of shorter gates.
Nickel mono-silicide (NiSi) technology appears to be emerging as a dominant solution to very narrow line polysilicon gates because it provides superior sheet resistance (Rs) for narrow line polysilicon gates, less junction leakage, less silicon (Si) consumption, and can even improve the drive current (Idsat) of an NFET or PFET.
There are, however, some concerns about NiSi because it may not form completely or at all when the single crystal Si or Si containing substrate is under tensile stress and instead, undesirable nickel di-silicide (NiSi2) forms. NiSi2 is undesirable because it increases the resistance of the silicide. Moreover, faceted NiSi2 may form deeply in the Si substrate thereby producing junction leakage. In addition, NiSi2 can easily form over a wide temperature range. For example, Ni will form epitaxial NiSi2 on a p-type Si crystal substrate as low as 225° C., which decreases the process window.
The tensile stress in the single crystal Si or Si containing substrate may be due to the p-type dopant atoms in the substrate. For example, boron is commonly used as a p-type dopant atom in Si. Boron has a smaller atomic radius than Si, which causes strain in the Si crystal lattice. Tensile stress in Si may also be due to geometry and thermal effects.
Accordingly, methods are needed which allow NiSi to be implemented successfully in modern integrated circuit and semiconductor device fabrication.